1. Field of the Invent
The present invention relates to an organic electronic material, and an electrophotographic photosensitive member having superior electrophotographic performances attributable to the employment of the material.
2. Related Background Art
In recent years, function-separated electrophotographic photosensitive members, in which the function of generating charges and the function of transporting charges are shared by respectively separate electronic materials, have brought about a marked improvement in the sensitivity and durability properties for which conventional organic photosensitive members have been considered to have disadvantages.
Such function-separated electrophotographic photosensitive members allow a wide range of selection of materials for charge-generating materials an charge-transporting materials, and hence can also be advantageous in, e.g., that electrophotographic photosensitive members having the desired performance can be produced with a greater ease and at a low cost.
As the charge-generating materials, various materials are known, including azo pigments, polycyclic quinone pigments, cyanine dyes, squaric acid dyes and pyrylium salt dyes.
Of these, azo pigments have the advantages that they have a high light-fastness, have a high charge-generating ability and can be synthesized with ease. Hence, many materials have been proposed.
As for the charge-transporting materials, known materials are exemplified by the pyrazolone compounds as disclosed in Japanese Patent Publication No. 52-4188, the hydrazone compounds as disclosed in Japanese Patent publication No. 55-42380 and Japanese Patent Application Laid-open No. 55-52063, the triphenylamine compounds as disclosed in Japanese Patent Publication No. 58-32372 and Japanese Patent Application Laid-open No. 61-132955, and the stilbene compounds as disclosed in Japanese Patent Applications Laid-open No. 54-151955 and No. 58-19804.
However, almost all of the known charge-transporting materials noted in the above, in particular, the charge-transporting materials used in organic electrophotographic photosensitive members practically used, have the properties of transporting positive holes.
When a charge-transporting material capable of transporting positive holes is used in an electrophotographic photosensitive member comprising a conductive support and, provided thereon, a charge generation layer and a charge transport layer in this order, i.e. having the conventional structure most commonly used, the polarity of the primary charge to the photosensitive member is negative. When the photosensitive member is negatively charged, ozone is generated. This ozone has a bad chemical bad influence on photosensitive members.
Now, as a countermeasure to the deterioration of photosensitive members due to the ozone generated in negative charging, a proposal has been made in, for example, Japanese Patent Applications Laid-open No. 61-753555 and No. 54-58445 on an electrophotographic photosensitive member comprising a support and, provided thereon, a charge transport layer and a charge generation layer in this order.
Since, however, in the electrophotographic photosensitive member with such layer constitution, the relatively thin charge generation layer is provided as an upper layer, a serious deterioration of performance is caused by the wear that accompanies repeated use.
When a photosensitive member is provided with a protective layer made of an organic insulating material for the purpose of preventing such wear, it has been impossible to maintain stable performances because of unstable potential after repeated use.
Under such circumstances, it has been sought to develop an organic electronic material capable of transporting electrons. Conventionally proposed charge-transporting materials capable of transporting electrons include, for example, 2,4,7-trinitro-9-fluorenone (TNF), the dicyanomethylenefluorene carboxylates as disclosed in Japanese Patent Application Laid-open No. 61-148159, the anthraquinodimethane compounds as disclosed in Japanese Patent Applications Laid-open No. 63-70257, No. 63-72664 and No. 63-104061, the 1,4-naphthoquinone compounds as disclosed in Japanese Patent Application Laid-open No. 63-85749, the diphenyldicyanoethylene compounds as disclosed in Japanese Patent Applications Laid-open No. 63-175860 and No. 63-174993, and the diphenoquinone compounds as described in The Proceedings of the 58th Springtime Annual Meeting of Japan Chemical Society (31H38), 431 (1989).
However, positive-charge photosensitive members making use of these charge-transporting materials capable of transporting electrons have been unsatisfactory in view of their residual potential after repeated use, their production cost and the compatibility with organic solvents and binders.